Steps

1. How to initialize a Sequence of donuts

The code below shows how to initialize a Sequence of Donut elements of type String.

println("Step 1: How to initialize a Sequence of donuts")
val donuts1: Seq[String] = Seq("Plain", "Strawberry", "Glazed")
println(s"Elements of donuts1 = $donuts1")

You should see the following output when you run your Scala application in IntelliJ:

Step 1: How to initialize a Sequence of donuts
Elements of donuts1 = List(Plain, Strawberry, Glazed)

2. How to initialize another Sequence of donuts

The code below shows how to initialize another Sequence of Donut elements of type String .

println("\nStep 2: How to initialize another Sequence of donuts")
val donuts2: Seq[String] = Seq("Vanilla", "Glazed")
println(s"Elements of donuts2 = $donuts2")

You should see the following output when you run your Scala application in IntelliJ:

Step 2: How to initialize another Sequence of donuts
Elements of donuts2 = List(Vanilla, Glazed)

3. How to create a List of donuts initialized using the two Sequences from Step 1 and Step 2

The code below shows how to create a List of donut elements and initialize the List by using the two donut sequences from Step 1 and Step 2 respectively.

println("\nStep 3: How to create a List of donuts initialized using the two Sequences from Step 1 and Step 2")
val listDonuts: List[Seq[String]] = List(donuts1, donuts2)
println(s"Elements of listDonuts = $listDonuts")

You should see the following output when you run your Scala application in IntelliJ:

Step 3: How to create a List of donuts initialized using the two Sequences from Step 1 and Step 2
Elements of listDonuts = List(List(Plain, Strawberry, Glazed), List(Vanilla, Glazed))

NOTE:

• We end up with a List containing two inner lists: List(List(Plain, Strawberry, Glazed), List(Vanilla, Glazed))
• What if you need to produce a single List of donut elements as opposed to having a List with two inner lists? We can achieve this using the flatten method as shown in Step 4 below.

4. How to return a single list of donut using the flatten function

The code below shows how to use the flatten method on the List of donuts which contains two inner donut lists and return a single donut List of type String.

println("\nStep 4: How to return a single list of donut using the flatten function")
val listDonutsFromFlatten: List[String] = listDonuts.flatten
println(s"Elements of listDonutsFromFlatten = $listDonutsFromFlatten")

You should see the following output when you run your Scala application in IntelliJ:

Step 4: How to return a single list of donut using the flatten function
Elements of listDonutsFromFlatten = List(Plain, Strawberry, Glazed, Vanilla, Glazed)

NOTE:

• By using the flatten method, we were able to collapse the donut String elements into a single list.

5. How to append the word Donut to each element of listDonuts using flatten and map functions

The code below shows how to use the flatten method followed by the map method to produce a single List of donut elements where the word Donut was appended to each element.

println("\nStep 5: How to append the word Donut to each element of listDonuts using flatten and map functions")
val listDonutsFromFlatten2: List[String] = listDonuts.flatten.map(_ + " Donut")
println(s"Elements of listDonutsFromFlatten2 = $listDonutsFromFlatten2")

You should see the following output when you run your Scala application in IntelliJ:

Step 5: How to append the word Donut to each element of listDonuts using flatten and map functions
Elements of listDonutsFromFlatten2 = List(Plain Donut, Strawberry Donut, Glazed Donut, Vanilla Donut, Glazed Donut)